The invention relates to a direct electrical drive for a wheel set of a vehicle. The vehicle is in particular a rail vehicle such as for example a train, a motor car, a locomotive, or a streetcar. The Offenlegungsschrift DE 100 47 911 A1 discloses a drive for a wheel set of a vehicle, having two wheels disposed on a wheel set shaft. The wheels can be driven by at least one internal rotor motor which encompasses the wheel set shaft. The internal rotor motor includes a stator and a rotor. The tubular rotor has permanent magnets on its surface. When using the direct electrical drive for rail vehicles for example, damage to the wheel set shaft during operation cannot be excluded.
Direct electrical drives have an electric motor constructed in particular as a synchronous motor or asynchronous motor. Despite their good efficiency, the rotor of synchronous motors as well as asynchronous motors encounters losses. As the rotor increasingly heats up, the efficiency of the electrical machine, like for example of the synchronous motor or asynchronous motor, declines.